1. Field of the Invention
This invention relates generally to backing blocks for abrasive coated belts used in traveling-belt sanding machines. More particularly, the invention relates to a shaped backing block having improved wear and heat dissipation characteristics and a superior smoothness of the belt contacting portion thereof.
2. Description of the Prior Art
It has been known in the past to use shaped backing blocks to press an abrasive-coated traveling belt against articles of wood in the making of moldings, furniture, and the like. When a backing block is pressed against the back of a sanding belt, which may be moving anywhere from 2500 to 5000 ft/min., considerable heat is produced by surface friction between them. This friction and the heat generated thereby causes deterioration of the block, expansion thereof (depending on the block material), uneven wear, and shortens the life of the belt. Additionally, the dusty environment created by the sanding operation adds to the wear on the backing block and the back of the belt and if steel or any iron alloy backing blocks were used a fire hazard would exist because of the possibility of sparks which might ignite the dust particles.
Heretofore, backing blocks have been formed according to standard practice either from a block of solid material such as wood, babbit-type material, plastic, glass, or a relatively more resilient material such as hard rubber, or hard block felt. The blocks were shaped by machining or otherwise forming on one face of the block a reverse of the profile of the piece to be sanded. This involved painstaking and laborious shaping and fitting to obtain satisfactory accuracy.
Due to the rapid wearing and deterioration of the blocks formed of the materials heretofore employed and, since a different backing block having a particular profile must be provided for each different shaped piece to be sanded, the problem of forming and maintaining an adequate supply of these backing blocks has been burdensome and expensive, especially in continuous sanding operations where relatively heavy sanding pressures are used.
U.S. Pat. No. 2,717,422 relates to a method and means for forming a sanding block. The block is characterized by a pressure face liner formed of a dimensionally stable plastic material and bearing on its face an impression of the wood molding profile to be sanded.
U.S. Pat. No. 2,624,160 relates to a lubricating means for platens or backing plates to reduce friction between the backing plates and the back of a traveling belt abrasive grinding machines. The lubricating means comprises a solid lubricant held in a pattern of grooves formed in the face of the backing plate.
U.S. Pat. No. 2,633,679 relates to a facing sheet affixed to a shaped block for pressing a traveling abrasive-coated belt against a work piece. Glass beads are adhesively affixed to the facing sheet to form a non-continuous pressing surface, thus reducing materially the frictional drag between the pressing member and the back of the belt.
U.S. Pat. No. 3,685,219 relates to a contour-abrasion means and method wherein a contoured back-up member for the adhesive-coated belt is provided with holes extending inwardly from its face to an air-supply channel. Air fed through the holes produces a thin air cushion for the belt to ride on.
U.S. Pat. No. 2,431,822 relates to an abrasive belt polishing machine which utilizes a contoured cylindrical roller to engage the side of a traveling abrasive-coated belt to press it into engagement with the surface of the work piece.
U.S. Pat. No. 2,934,279 relates to the production of ground wood pulp wherein a back-up plate is used to press an abrasive-coated traveling belt against a log or billet. It is stated in this patent that the heat generated by friction between the face of the pressure plate and the back of the belt may be dissipated by the introduction of water therebetween through small holes or pores in the plate.
It is apparent that the prior art disclosures have not provided a backing plate for pressing a traveling abrasive-coated belt against a work piece wherein, the backing plate would have a highly polished wear surface and good heat-dissipating characteristics, thus prolonging the life of the belt and the plate; a low rate of expansion and wear to maintain the shape of the sanded parts and to reduce dramatically the cost, time, effort, and inventory required to maintain an adequate supply of backing plates.